I. Field of the Invention
The present invention relates generally to the fields of diagnostic and screening tests. More particularly, it concerns improved methods for the detection of early anti-HIV antibody in a sample, as well as early diagnostic tests to detect human immunodeficiency virus exposure or infection in infants. An additional aspect of the invention concerns methods for detecting HIV in idiopathic chronic lymphopenia patients. The invention also relates to the field of recombinant proteins, as particular recombinant proteins and recombinant protein composite preparations of several human immunodeficiency virus strains are disclosed. The invention also relates to the field of commercial diagnostic and prognostic assay plates and kits, as assay plates designed to detect an early anti-HIV antibody that include the described recombinant human immunodeficiency virus antigen or preparations of human immunodeficiency virus infected cell isolates are described.
II. Background of the Invention
Patients infected with human immunodeficiency virus (HIV) are known to eventually mount a humoral immune response to the virus. The production of anti-HIV antibody is one marker used to detect this response. In some studies, anti-HIV antibody has been reported to be more reliable for diagnosis than either HIV culture or HIV antigen detection in patient samples.sup.1,2. Consequently, anti-HIV antibody detection tests are the most common method of diagnosis of infection. Both EIA and Western blot assays are currently used in the detection of anti-HIV antibody.
Unfortunately, a degree of unreliability continues to exist with the use of conventional anti-HIV antibody screening methods, such as by conventional EIAs. Thus, a further confirmatory test, such as a Western Blot (WB) or fixed-cell immunofluorescence assay, have become recommended additional testing procedures.
Despite these and other additional precautionary testing measures, a number of studies report the existence of a seemingly silent period of HIV infection during which antibody to the virus is not detectable even after exhaustive testing. This period reportedly extends from the point of infection to the time infection is detectable through conventional sero-conversion assays. This silent period has been reported to persist anywhere from a few months to as much as two and one-half years before infection is detectable by conventional EIAs and Western blot assays.
While not always successful, culturing of peripheral blood lymphocytes to amplify HIV does provide for detection of the virus when anti-HIV antibody cannot be detected by conventional EIA or WB. However, several recent studies using PCR-based HIV detection methods continue to report the existence of PCR(+)positive, sero(-)negative cases in high-risk populations.sup.10-17. Nevertheless, PCR usually does detect infection before conventional sero-conversion methods, with the aforedescribed period of silent infection being reduced by approximately one month, at least in some cases.sup.18.
The rate of HIV transmission in negatively tested blood, using conventional testing methods, continues to persist at a relatively constant rate.sup.25. For example, HIV-1 transmission from seemingly "seronegative" blood using EIA conventional methods, continue to be reported.sup.21-23. Donated organs also constitute a source of HIV disease transmission, with HIV infection being diagnosed in recipients of organs from individuals whom, again, test HIV seronegative by conventional assays.sup.24.
Retrospective studies have reported that early donor education and self-exclusion measures has reduced the rate of disease transmission.sup.26. However, such exclusion methods together with antibody testing, while hopefully reducing the probability of at least some false negative results.sup.27, provides only a partial and imperfect solution to the problem in at least a small subset of reported HIV cases.
Some studies report the presence of HIV specific T-cells in high risk individuals testing negative with conventional EIA, WB, and PCR based detection techniques.sup.28,29. Other reports have identified the existence of B-cells which produce HIV-specific antibodies in vitro that are present in EIA-negative, WB-negative, high-risk subjects.sup.30. While these approaches present possible alternatives, for testing, they are relatively complex and difficult procedures, and are thus impractical for large-scale clinical screening. The expense and time associated with this type of testing again leaves a need in the medical arts for a reliable and practical HIV screening and detection approach.
Early HIV infection of infants is a particularly troublesome problem. Current technology renders it difficult to diagnose whether an infant less than 18 months of age is infected, absent development of overt clinical symptoms. Conventional HIV serological tests for anti-HIV antibody are inadequate for detecting infection in an infant because the antibody detected is not necessarily that of the infant, but is that of the HIV-positive mother. This maternally derived antibody typically persists for up to 21 months in the infants system.sup.34.
Neither IgA or IgM antibody cross the placenta. Hence, studies in children have emphasized the detection of IgA and IgM as indicators of infant HIV infection. In one study, both HIV-specific IgA and IgM were found in infants up to 12 months of age born to sero-positive mothers, with twice as many samples yielding IgA anti-HIV compared to IgM (66% vs. 33%).sup.35 using conventional screening assays (WB, EIA).
Currently, approximately 50% of infected infants can be identified at birth, approximately 90% by 3 months of age, and almost all by 6 months of age using combination HIV culture, PCR, IgA antibody tests, and p24 antigen tests.sup.38. However, the fact that HIV can be detected in only one-half of infected infants at the time of birth again points to the continued need for improved early HIV detection in infants.